Messages - emag

A long exposure noise reduction method for astrophotography is the use of a 'dark frame'. In principal it's similar to LENR but the practice is different. A number of images are captured with the camera lens/telescope cover in place (i.e. - dark frames), I typically take them when I'm finished with my imaging and am putting my equipment up. The exposure length is the same as that used for the images ('light' frames). The dark frames are averaged in post and a master dark frame created which is then subtracted from each light frame prior to stacking the lights. Ideally, the darks are captured at the same temperature the lights are captured at. I suppose it would be possible to create a library of master darks at various temperature ranges, but the sometimes (or usually?) random nature of the dark frame noise might preclude that. In addition to the dark frames, a series of bias frames are also captured, similarly averaged and subtracted. These are dark frames at short exposure taken to create a master bias frame that hopefully captures the readout noise which is also subracted from the light frames prior to stacking. With the D60 years ago, Canon was first out the gate with a low noise sensor capable of astrophotography....the reason I and many others adopted Canon DSLRs for astro.

Reason I mention all this is that if you're contemplating a lot of long exposure work, you may find these techniques useful. For exposures of a few seconds, LENR is probably more practical. My astro work involves exposures of 90 seconds to 10 minutes, LENR is just not a good option at that point.

Both work well for me and my uses.....YMMV. If you just want to get something decent that is actually available so you can play around with it then I would recommend both of these. Purists may cringe but they are welcome to PM me so I can give them my mailing address for that elusive Lee Big Stopper and other top shelf items they want to send me.

I was recently in my local BestBuy and found a 77mm CPL and 77mm ND3 that included a 72-77 adapter. Reasonable price and they work on all of my larger lenses including the 300/4L and 400/5.6 and most happily the Tokina 11-16/2.8.

I would strongly recommend against a variable ND, there may be some that do not exhibit the cross effect at higher density levels but the vast majority do, particularly any of the lower priced ones.

I also have an (equivalent to) Expodisk and have used it extensively. It is indeed quicker than the Color Checker Passport for setting a custom white balance.......BUT......the passport has so many more uses and is just as simple to carry. I've really taken a shine to it since I began using it. You can set up custom camera profiles in Lightroom for various lighting conditions (sunny, clouds, rain, twilight, deep shade, etc.), shoot Raw and select the correct profile in post. Much less tweaking is needed with such a work flow. Want to warm skin tones a tad? Click on the appropriate warming white balance block on the image of the Color Checker. IIRC, there have been posts on CR from colorblind photographers here on CR who use the Passport to ensure proper color.

From the you-think-that's-bad department......Florida Panhandle here. In August, 90% humidity would be considered arid. Just in case the unimagineable occurs and the sky clears up for one evening, we have Ninja mosquitoes just waiting for us to be foolish enough to set up scopes and cameras. In all my years here, I have once and only once enjoyed astrophotography on an August night. It was while a hurricane was crossing central Florida and sucking dry air over Pensacola, dropped to the low 60's that night, it felt frigid. A few weeks later we were hit by Hurricane Ivan, took out the U.S. Interstate 10 bridge over the bay and knocked out power for weeks. But oh how gourgeous the skies were after that.....dark, clear, no light pollution. We slept in the screen room because it was too hot in the house, I still recall seeing the Pleiades rising through the branches of the leafless trees in my back yard.

Some examples, I've posted modified links instead of embedding, just change (dot) to . and they should work fine.

with G2 and GentLED....... youtube(dot)com/watch?v=ahaQVk0iv20&list=TLitG5fo8Po8cwith modified 40D......... youtube(dot)com/watch?v=sHRqxuHc1XU&list=TLQkYow0aU2Pkwith 60D.....daylight........youtube(dot)com/watch?v=4tqw1SX4NK8&list=TLQkYow0aU2Pk60D astro timelapse..........youtube(dot)com/watch?v=WBwNGcLGH1g40D timelapse of 60d taking a timelapse....youtube(dot)com/watch?v=KHzBE5y08DQPentax W90 on motorcycle.....youtube(dot)com/watch?v=tY5QRwiRMGo..and on my scooter for the work commute.....youtube(dot)com/watch?v=7-vbMcI6Kmg

If you are only doing daylight timelapses, there are quite a few cameras (including non-Canon) to choose from. For example, I have a Pentax W90 that has a timelapse function built in, is waterproof and light enough to fly with a kite and Picavet rig. Image quality is of course nowhere near DSLR but in truth not too shabby. I've strapped it to my motorcycle for several hours of riding, it just keeps on shooting until the battery dies or the card is full. My old Canon G2, although quite long in the tooth, is timelapse capable with a GentLed IR trigger. Only 4MP, but for timelapse movies the individual frames really don't need to be huge. For astro timelapses I use my 60D and modified 40D. I'll consider shutter replacement when it becomes an issue, but until then, I bought these cameras to use them. Like my knees, they won't last forever.

A drawback to using those high f-ratios like f/22....it will show any dust dirt whatever specs that are on your sensor, in addition to refraction effects. f/11 is more forgiving. The EF 28-135 will go to something like f/36 (32?) on the long end - great for checking sensor cleanliness, lousy for photos.

Everybody loses their mojo once in a while. I used to talk to Ron Rico about it, nowadays I find Jameson's helpful. In other words.......don't sweat it. One of my lifelong passions has been astronomy, but there have been extended periods where I did little (couple years here and there). When the passion returns, it does so with a welcome vengeance. The moon interferes with the deep sky astrophotography I prefer, but every so often I find myself doing visual with the moon with a high power eyepiece. Two hours can pass with no perception of the time.

You will get your mojo back. If you don't, you never had it in the first place.....but I don't believe that and neither do you. Think of it like writer's block.